Corvette Engine Build - The Power Principal

An Economical 383 Engine Build Anyone Can Do

Chris Petris Dec 8, 2009 0 Comment(s)
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Now it's up to us to check for proper bearing clearances. The snap gauge measures the crankshaft main and rod bearing bore diameter. This tool is then measured with a dial caliper to find the inner-bore diameter. When you're looking for 0.0015-0.003 bearing clearance, accurate tool usage is important and takes some finesse. As bearing clearances increase, the oil pressure drops. Likewise, tight clearances increase oil pressure.

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Our crank journal measures 2.100 inch using the dial caliper at each main bearing journal. The main bearing bore measured 2.098, so we end up with 0.002 on No. 1 and No. 5 main bearing for clearance. The No. 2, No. 3, and No. 4 main bearing clearance was 0.0015, which is tighter; it's common to find the center bearings to be tighter. If you have a 0.003 bearing clearance, a high-volume oil pump and 15W40 oil will be necessary or low oil pressure will be the norm.

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Building any engine takes care, and when you're building a performance engine, ring endgaps are crucial for long engine life. If the rings are too loose, compression is lost. Too tight, and the rings can drag or lock in the cylinder as heat builds. Worse yet, they can break and cause piston failure. We push the ring down past midway in the cylinder and measure the gap.

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Now that we know the rings are too tight in the cylinder, our Childs & Albert precision ring filer is put to work. We use a hand-powered filer, holding the ring flat against the rotating wheel. The wheel should be rotated towards the outside edge of the ring to avoid chipping the outside edge that seals against the cylinder. This is tedious work, and care must be taken because it's easy to go too far. Once you do one ring, usually the same amount must be removed from each ring, so count the revolutions of the filer to know when you are close.

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Now we take a jeweler's file and deburr the edges of the ring so the piston isn't gouged and the cylinder wall doesn't get scratched. Don't chamfer the edges, just knock the edge off from the grinder. We talked about the possible addition of nitrous for the street/strip engine, so we would need to file the rings for more clearance to compensate for the additional cylinder heat.

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This may seem petty, but we grind each ring to fit each cylinder, then place them on their respective piston, then on the workbench as shown. Each cylinder should be the same bore size in theory, but there are variations, and every little bit helps. Having everything in its place makes the most sense when assembling components since there is less chance of forgetting something.